fix: query_param_matcher no longer mutates the caller's params dict

[gaoflow]

Problem

query_param_matcher converts int and float values to strings so they can
be compared against URL query-string values (which are always strings). However,
this conversion was done in-place on the dict reference obtained via
params_dict = params or {}, which aliases the original dict when a non-empty
mapping is passed. As a result, every numeric value in the caller's dict is
silently overwritten with its string equivalent:

params = {"page": 1, "ratio": 0.5}
matchers.query_param_matcher(params)
# params is now {"page": "1", "ratio": "0.5"} — mutated!

This is surprising behaviour that can cause hard-to-debug failures when the
same dict is inspected or reused after the matcher is created.

Fix

Copy the mapping into a fresh dict before the normalisation loop:

-    params_dict = params or {}
+    params_dict = dict(params) if params else {}

A regression test (test_query_param_matcher_does_not_mutate_input) is
included.

This pull request was prepared with the assistance of AI, under my direction and review.

[markstory]

Could you also add a note to the CHANGES file about this fix?

[gaoflow]

Added the CHANGES entry in 03e670a.

Verification:

uv run --with pytest --with pytest-asyncio --with requests --with urllib3 --with pyyaml --with types-PyYAML python -m pytest responses/tests/test_matchers.py::test_query_param_matcher_does_not_mutate_input -q
# 1 passed

git diff --check
# passed

I first tried the system python -m pytest, but the local global pytest plugin stack is broken (pytest_pylint missing tomlkit, then a pytest/pytest-asyncio version mismatch), so I used an isolated uv run --with ... environment for the focused test.

[gaoflow]

Rebased onto current master and resolved the CHANGES conflict while keeping both the upstream #798 entry and the #801 note.

Verification after the rebase:

uv run --with pytest --with pytest-asyncio --with requests --with urllib3 --with pyyaml --with types-PyYAML python -m pytest responses/tests/test_matchers.py::test_query_param_matcher_does_not_mutate_input -q
git diff --check origin/master...HEAD